Tempering of hollow glass articles



Jan. 6, 1942; J. B MITFORD TEMPERING OF YHQLLOWYGLASS ARTICLES Filed Nov. 2, 1939 F/aZ.

//v YEA/701?. Jay/v BA was M1 TFO RD ATTORN X Patented Jan. 6, 1942 I WW; m HOLLOW omss anirrorjns i1 .mm "Bawden' Mitfol-d, ltainhilh-England, as-

signor'to Corning Glassworks, .a company of New. York. I

Application November 2,1939, S erialNo. 'In Great BritainOctober 2 0, 1938 I acijaimsg (cue-8'9) This invention relates to the toughening of glass bottles and has for'its object an improved method of chillingtheheated bottle b gaseous chilling'medium so as to toughen it toa; high de-f gree and so that the outer and inner surfaces are 1 in substantially equal compression.

Hollowarticleshave been toughened by'blow that there is [a pressurepf air insidethe bottle.

This difference isl'material' when low pressure air, with large-jet holes is used, b'ut is less-important than the previously mentioned facts when high pressures, such-as .50 lbs. per sq. in.'are used. ']It' has 'beenfound'that; to toughen a. bottle such asia milk. bottle symmetrically, from one ing air on their outer surfaces by external jet tubes and on their inner surfaces by intemal jet :tubes, as described, in the specification of Letters Patent No.'2-,054,595, and the toughening so DI'O- and a half to two' times" as much'ainshould be ,directedjjagainstthe inner surface as against the outer, surface, And, since the cooling effect of a v :"given" volume ofair varies largely with the veduced is satisfactory for many purposes, provided v that the article is open at both ends or, if closed at one end, has'amouth at least as largeas its length. Bottles such as milk bottles, however,

Jinnerand outer' jet. holes with. the sam Velocity. Thus,*by'-way of example, if theinner and outer jet tubes are "connected to the sameairgsupply when so toughened hitherto are found notftow' resistance to thermal shock.

Applicants have found that this deficiency in strength isrdue to the compression in "the inner surface being. less than that in theouter surface, so that the layerof maximum tension in theglass is not the central layer.

I Heretofore it has been the practice in toughening glass byair jets to produce stresses symmetri- .cal about the central layer by blowing air on the have the strength of the toughened flat glass'of I commerce and, more particularlyv are deficient in two surfaces at equal. rates per unit of surface.

It has been found in the case of bottles, that this "practice does not abstract heat at an equal rate I from the-outer and. inner surfaces, and further, it-h'as been found that it is necessary to abstract' 5 heat by the air at. a higher rate from the inner r surface than from the outer surface.

The reasons for these facts are, first, air blown into a bottle has all to escape from the mouth,

and therefore there isa rapid flow of air along the length of the bottle from the bottom towards I the mouth? This flow is. at right angles-to the jets of air directed against the inner surface, and therefore divertsthe jets and diminishes the velocltywith which the air strikes the surface. 3 Thereby the cooling efliciencyofthejetsaisdiminished, so. thatv a given jet of airabstracts-heat. at alesser rate when. directed against the-inner surface than when directed, against thev outer. surface;.- Secondly, during the. first portion of the cooling, a substantial portion of the cooling of the outer surface is effected; by radiation to the: cold} surroundings, The inner surface, however,

is exposed only to itself,,and cannot-appreciably cool by radiation. Consequently, as compared: with the outer-surface, to secure an equal rate of fall of temperature, heat must be: abstracted by the air at a greater rate from the inner-surlocity of the air in the 'jet, it is assumed, in mak-.

ing this comparison, that the airissues from the and the, sarn'e size of jetholejis used, there should 'be from one andahalf to two timesas many jet holes in the inner as in the outer jet tubes. ,It is assumed further in making the comparison, that thejets are all directed normally to thesurface, since they are thenm'ost effectiveif" Q "Further, in order to secure uniformity of toughening from the 'base 'tothe'mouth of the bottle, it has been found necessary to distribute the blowing'non uniforn ly over the inner surface; by'directin'g a substantially greater volume of air' per unit of surface against the surface near the corner'f ormed by the junction of the. sides a and base: The-reason for'this is that air blown against any point of h the inside surface'has to travel towards the mouth, and there'isno tendency' for. it tov travel towards the base. Thereffore-the air has ac'ooling effect on all the wall surfacenearer to the mouth than the point of impact and no appreciablecooling-effect on any wall surface nearer tothe base of the bottle.

More uniforrncoolingis thus obtained by directing: a large. proportionof air against'the base part. of the bottle, since.all- -t'he air so directed has some cooling effect onthe whole surface;

Air should be: directed intothe-corner at the base, so asto-ensure: rapid movement of" air over the surface in the corner, and it has been found most effective in securing uniform cooling to ;.di1r ect-a larger volumeof airtper funitof surface face. There; is a third reason why cooling by air .iets is less effective on the inner surface than on the outer surface, namely that, for agiven: pressure of air supply.v a smaller difference of pressure. is available to produce a jet, for .the'reason against a the, inner wall for. a short distance from thejcorner away from the base; Such larger vol- 3 ume may also be directedagainst the surface of thebase nearthecorner..-

According" to f the invention, thefamount of gaseous: cooling medium blown against the inner "surface is greater than the amount blown against the outer surface to, anexten-t sufficient to secure that: the innerand outer surfaces: coolat. substantially;- the. samerate; .FurtherL -more heat is abstracted by the cooling. medium from the inner surface than from the outer surface.

. In the accompanying drawing, Figure ,1 is a. side view of the blowing apparatus, showing the The drawing shows a bottle of the typesinseda V The object of the invention is to obtain a high degree of toughening, but it is often desirable to for the distribution of milk, having a. diameter avqldwmh ih a, degree that the fracture of the mately cylindrical body Portion reaching, up to .the line AA of Figure 2. and a tapering neck portion. The bottle I rests on an asbestos disc I held in a frame 3 adapted to be rotated in the hearing I by a pulley 5. A single jet tubeji passes through the frame 3 and is supplied with air .by the pipe I, to direct the air against the bottom of the bottle. The disc'i has acentral hole I of approximately the diameter of the bottie, but with four inwardly projecting lugs 9 on which the bottle rests,while four asbestos pads less than twice its length, and with an approil bottle is eiplosive. A high degree of toughening which is Justshort of giving an explosive fracture, gives the bottle nearly the maximum resistance to thermal shock.

I] retain the bottle in position. Nearly all the bottom of the bottle is therefore exposed to the by turning the arm H, the blowing tubes are lifted clear of thebottle. The arm l6. shown broken off, is adapted totake a couruterweight,

and a stop I1 isprovided on which the arm I ,The inner and outer Jets are symmetrically placed with reference to the centre line of the bottle, so that their pressures against the sides of the bottle arebalanced, and the bottle is 1'0- tated so. as to secure uniformity of cooling. Ro-

. tation of the blowing tubes while the bottle is edindependentlyto the air supply,'with valves in the connections, so that the. airpressures in the y, inner and outertubes maybevaried.

7 Where, in the-claims, relativeamounts of air l are specified, it is assumed that the ,air pressures mately.equal'velocities.

rests when the blowing tubes are in operative position. The inner and outer blowing tubes are blowing tubes II and I! are provided with jet holes which are indicated on the drawing by lines it from the inner tube and ll ifrom the outer tubes, these lines indicating the direction of the jet from each hole. For the sake of clearness, the lines I! are shown as all issuing from the inner tube II in one planebut, in practice,

the jet holes are more conveniently distributed round the tube.

Assuming all jet holes to be of the same size,

about 75% more air'is blown against. thesinner "surface from the -30 jet holes in the inner tube It than from the 17 jet holes in the outer tubes I2. Further, considering only the bodyportion up to the line AA, there. are 12 jet holes blow-' ing against'the lower half and 16 jet holes blowing.against the lower half including the base,

3 and 8 Jet holes blowing against the upper half. Further, considering the portion up to the line B- -B of Figure 2, which isone-sixth of the total height of the bottle; about 40% of the total amount of air from the inner tube is blown against the wall and base up to this line, In practice it is generally more convenient to have a smaller number of holes of larger'size in the inner tube.

' what I in the inner and outer tubes are approximately equal, 'sothat the; air jets issue,v with. approxi- V IiTde clare that claim and desire-to secure by Letters Pat- Having descrlb'edmy invention,

.ent is: 1

1. A process of tempering ahollowglassarticle having a closed base and an open topand having a height at least twice its diameter, byheating the same to a temperature adjacentits softening point and rapidly chilling the heated article by directing jets of gaseous chilling fluid against its inner and outersurfaces which is characterized by directing a greater amount of chilling fluid against its inner'surfaces than against its outer surfaces, and directing. more than half of the chilling fluid: that is directed-against its inner surfaces against .the lower-half thereof; 3

i 2; A processo'f tempering a-hollow glass "article having a closed base and an open top and having a height at least twice its diameter, by heating the same to a temperature adjacent its softening pointand rapidly chillingtheh'eated' article by directing jets of gaseous chillin'g' fluid against its inner and outer. surfaceswhich isfcharacterized against its inner surfaces than against-its outer surfaces; and directing at least two-thirds of the chilling'fluid that is directed against the inner surfaces of the article against the base and lower The actual quantities of air blown against the I inside and the outside and .the distribution of air in the inside which give the best resultcan only be found'by trial, preferably by subjecting the bottle to thermal shock tests. The example given indicates a satisfactory distribution for the bottle shown, and will serve to illustrate more clearly than would a general description the a'p-- proximate distribution required to satisfactorily half'of the inner surfaces;thereof.',, H i

3. Aprocess of tern a hollo'w'glass article having a closed base and'an open top and having a height at: least twice'its diameter, by heating the same to a temperature adjacent its softening point and rapidlychilling the heated article by directing jets of gaseous chilling fluid against its inner and outer surfaces which is characterized by directing a'greater amount of chillingfluid against its inner surfaces than against its outer surfaces, and directing at least 40% of the chilling fluid that is directed against the inner surfaces of the article against the base and a zone JOHN BAWDEN m'rr'oan. 

